1. Field of the Invention
The present invention relates to a jet coating apparatus for applying a coating mix onto a moving web in a non-contacting manner in ambient pressure without the presence of a pressurized coating chamber.
2. Description of the Prior Art
EP patent application No. 0,466,420 which corresponds to U.S. Pat. No. 5,186,753, discloses a jet coating method in which a jet coating apparatus is employed for applying the coating mix on the web and the final coat weight is controlled by means of an actual doctor blade. The coating mix is applied on the web in ambient pressure without a pressurized coating chamber. The jet coating apparatus of this reference applies the jet of coating mix in the direction of movement of the web. However the jet coating unit of the apparatus is tiltable about its tip, thus permitting, when necessary an almost perpendicular application of the coating mix jet onto the web. Particularly at high web speeds (above 1000 m/min), problems are caused by entrained air carried over in the web and applied coating mix, resulting in inferior coat quality, mottling and possibly uncoated areas. Moreover, the air entrained in the web causes unevenness of the applied coat. Sufficient penetration of the mix into the web is also difficult to attain.
Further, known in the art from FI patent application 89 0249 (U.S. Pat. No. 5,104,697) is a brush coating apparatus in which the coating mix is applied onto the web via a channel of narrow slot orifice with the help of a predoctoring blade tilted to a narrow angle with respect to the web. Typically, the embodiment also incorporates a doctor blade arranged at the same backing roll. This embodiment has problems in some operating situations particularly when the tension distribution of the base web is uneven, whereby the two points (coating apparatus and doctor blade) contacting the web produce a deleteriously uneven distribution of cross-machine web tension between these two points. Such a situation causes runnability problems under certain conditions.